Fusible link circuit protective device

ABSTRACT

A thermally actuated switch having a pair of fixed contacts and a pair of movable contacts, the movable contacts being located on a pair of electrically conductive resilient contact carrying arms supported in cantilever fashion such that the movable contacts are located intermediate the ends of the arms for cooperation with a pair of fixed contacts, and a crossbeam member spring biasing the free ends of the spring arms into contact closing position. A fusible wire link is associated with the crossbeam for holding the movable contacts in engagement with the fixed contacts whereby the wire link fuses when a predetermined electric current is passed therethrough effecting snap-action release of the spring arms in unison to simultaneously open the paired contacts and electrically disconnect the line conductors of an electrical appliance from a power source.

United States Patent [72] Inventor Robert R. Gould, Jr.

Dayton, Ohio [21] Appl. No. 88,389 [22] Filed Nov. 10, 1970 [45] Patented Dec. 21, 1971 [73] Assignee General Motors Corporation Detroit, Mich.

[54] FUSIBLE LINK CIRCUIT PROTECTIVE DEVICE 5 Claims, 6 Drawing Figs.

[52] U.S. Cl 337/239, 337/407, 337/410 [51] Int. Cl. ll0lh 85/36 [50] Field oiSearch 337/239, 407, 410

[56] References Cited I UNITED STATES PATENTS 2,777,918 l/l957 Sears 337/15 295,760 3/1884 I-Iill 337/407 FOREIGN PATENTS 648,050 12/1950 GreatBritain ABSTRACT: A thermally actuated switch having a pair of fixed contacts and a pair of movable contacts, the movable contacts being located on a ,pair of electrically conductive resilient contact carrying arms supported in cantilever fashion such that the movable contacts are located intermediate the ends of the arms for cooperation with a pair of fixed contacts, and a crossbeam member spring biasing the free ends of the spring arms into contact closing position. A fusible wire link is associated with the crossbeam for holding the movable contacts in engagement with the fixed contacts whereby the wire link fuses when a predetermined electric current is passed therethrough effecting snap-action release of the spring arms in unison to simultaneously open the paired contacts and electrically disconnect the line conductors of an electrical appliance from a power source.

- PAIENTEDnEwmn 33629-166.

" ,SHEETZU'FZ' v V INVENTOR.

Roberi 1?. Goa/diff ATTORNEY FUSIBLE LINK CIRCUIT PROTECTIVE DEVICE This invention relates to a fusible link circuit protective device and more particularly to an inexpensive electric circuit protective fuse operative to simultaneously interrupt both lines of a power source to an electrical appliance or the like.

In the construction of .thermally responsive relays it is frequently necessary to provide a circuit protective device in which two or more fused current supply lines are required to be isolated from a power source when one line is disconnected due to an overload in the circuit. This may be accomplished by providing a separate fuse device in each line of a circuit, however, such an arrangement does not always insure that both lines will be fused such as when the amount of heat required to melt the fuses is unequal with the possible result that only one of the fuses is sufficiently heated to its fusing temperature.

It is therefore an object of the present invention for the provision of an inexpensive electric circuit protective device which is capable of disconnecting both lines from a power source simultaneously when an input of electric current is provided to an electrically isolated actuating mechanism.

Another object of the present invention is to provide a fusible link-type circuit protective device such that when an actuating current flows through the fusible link resistance wire which retains a pair of electrically conductive, cantilevered, contact carrying spring arms closed by means of a crossbeam joining the free ends of the spring arms such that when the wire link fuses the spring arm contacts are allowed to simultaneously return to their open circuit position and interrupt the power circuit. The spring arm contacts are located intermediate the free and fixed ends of the spring arms for fulcrumed contract with fixed contacts at an elevation below that of the spring arm cantilevered supports while the free ends of the spring arms engage stop lugs to provide ready calibrated positioning of the downwardly bowed spring arms.

An additional object of the present invention is to provide a fusible link circuit protective device that is capable of high ambient temperature operation due to the high melting temperature of the actuating fusible wire link while allowing for thermal expansion of the wire without materially reducing the positive closed contact pressure between the movable and fixed electrical contacts. 1

Further objects and features of the invention will be readily apparent from the following description, reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings:

FIG. 1 is a top plan view of a fusible link circuit protective device incorporating the features of the present invention;

FIG. 2 is a cross-sectional view taken along the lines 22 of FIG. I with the contact arms held in closed circuit relation by the fusible wire link;

FIG. 3 is a cross-sectional view similar to FIG. 2 showing the position of the contacts when the fusible wire link has been fused;

FIG. 4 is a top plan view showing the preferred embodiment of the invention with portions of the casing broken away for the purposes of illustration;

FIG. 5 is a cross-sectional view taken along the line 55 of FIG. 4;

FIG. 6 is a circuit diagram employing the circuit protective device of the invention.

In the drawings, and in FIGS. 1 and 2, particularly, one embodiment of the protective circuit device includes a housing 10 which is preferably formed of a suitable thermosetting plastic resin such as a phenolic material which is electrically insulating in character. The housing which may be box-shaped has a bottom wall 12, sidewalls l4, l6 and end walls 18, and a removable metallic cover plate 21 provided with a pair of outwardly directed securing tab portions 22 and 23. The housing 10 provides bearing means in the form of laterally paired longitudinally spaced first, second and third sets of raised bearing elements indicated at 24, 26, 27 and 28, 29 respectively, which are shown formed integrally with the housing. The first set of bearing elements are in the form of rectangular blocks 24, 25 formed integrally with the left hand end wall 20 and associated sides of the housing. The second set of bearing elements are intermediate blocks 26, 27 having inwardly facing semicircular portions extending in opposed relation from the sidewalls 14 and 16, respectively, while the third set of bearing elements are in the form of stop or calibrating lugs 28, 29 adjacent the end wall 18. It will be noted that the bearing blocks 24, 25 each have coplanar upper surfaces 24a and 25a positioned at an elevation which is a defined distance above coplanar upper surfaces 26a, 27a or intermediate bearing blocks 26, 27, respectively, and which in turn are positioned at an elevation which is a defined distance above the coplanar upper surfaces 28a, 29a of the stop lugs 28, 29.

Secured to the blocks 24, 25, in cantilever fashion are a pair of identical elongated single pole single throw switches having switch operating parallel cantilevered spring arms 30. 31 formed of electrically conductive material which in their unbiased or normal condition extend longitudinally in a horizontal plane as view in FIG. 3. The pair of spring arms 30, 31 are fixedly clamped at one end by terminal bolts 32, 33 respectively, to the upper surfaces 24a, 25a of blocks 24, 25. The terminal bolts 32, 33 threaded ends project from the underside of the bottom wall 12 and receive terminal binding nuts 34 so as to be externally accessible of the housing for the attachment of suitable lead wires. Each of the spring arms 30, 31 carries at a point intermediate its free end and its cantilevered mounting end control means or switch contact members 36, 37 which are electrically connected to their associated spring arms 30, 3] as by rivets 36a. Cooperable with the spring arm contact members 36, 37 there are fixed switch contact members, only one of which is visible at 38 in the FIG. 2 drawing, carried by terminal post members 40, 41 shown projecting from the underside of the base member and externally screw threaded to receive terminal binding nuts 42. The contact ends of the posts 40 and 41 are retained by securing nuts indicated at 44 in FIG. 2 and located in counterbores in the bearing boss surfaces 26a and 27a.

The free ends of the cantilevered spring arms 30, 31 are secured together by a crossbeam member indicated at 45 having a planar undersurface 46 and formed of suitable insulating material such as electrical porcelain. The crossbeam 45 is provided with a pair of integral spaced detents, 47 and 48 located to extend through apertures provided in the free ends of the spring arms 30, 31 respectively to maintain the arms in positively spaced parallel relation. The detents 47 and 48 are spaced to engage the pair of laterally spaced stop lugs 28, 29 upstanding from the bottom wall 12. The crossbeam 45 has a pair of spaced transverse raised ridges 53, 54 formed on either side of the midpoint of the crossbeam 45 defining saddlelike receiving means 55 therebetween for retaining a looped fusible wire link fuse element 56 therebetween. The free ends of the fusible wire link 56 extend downwardly to terminal means shown as a pair of spaced terminals 57, 58 sealed in opening in bottom wall 12 such that the wire link free ends extend through binding holes provided in the terminals 57, 58 and are electrically connected thereto in a conventional manner such as by an electrically conductive epoxy cement.

It will be appreciated that by means of the foregoing arrangement the spring arms 30, 31 normally maintain their movable contacts 38, 39 respectively out of engagement with their associated fixed contacts 38, 39 to an open position of the switch contacts as shown in FIG. 3. As seen in FIG. 2 the crossbeam 45 is operatively positioned to urge the spring arm free ends toward the bottom wall 12 to spring bias the closure of the contacts 36, 38 and 37, 39. The crossbeam detents 47, 48 engage the set of stop lugs 28, 29 for calibrating the engaged contacts of the device in its closed circuit operating position. The elevation of the fixed contacts 38, 39 together with the stop lugs 28, 29 establish the downwardly bowed flexure of the spring arms 30, 31. By virtue of being fulcrumed on the fixed contacts 38, 39 intermediate their free ends and their cantilevered mountings applicants device accurately positions the spring arms 30, 31 in the same concavely downward cylindrical space curve upon securing the free ends of the fuse wire link 56 to terminals 57, 58 as shown in FIG. 2 thereby requiring no further adjustment of the fusible wire link 56 during manufacture and subsequent operative use. It will be noted that this arrangement allows for ambient temperature compensation in that the fusible wire link can expand and contract without substantially affecting the required contact pressure between the contacts 36, 38 and 37, 39. A longitudinal partition member 50 is formed integral with the underside of the housing bottom wall 12 to provide for physical separation of the electrical lines connected to the terminal bolts 32, 33 and posts 40, 41.

A preferred form of the invention is shown in FIGS. 4 and to comprise a circuit protective device comprising a body assembly including a main body housing 61 and a cover plate 62. The housing 61 as in the case of the embodiment of FIGS. 1-3 described above is normally formed of an electrically insulating thermosetting plastic resin such as phenolic material. The cover element 62 is removably secured to the main body or housing 61 by suitable fasteners (not shown) and cooperates with the housing 61 to provide a fusible link protective device chamber in which the mechanism is mounted. The housing 61 is rectangular or box-shaped having a bottom wall 63, sidewalls 64, 65 and end walls 66, 67 and for reception of the cover plate 62 which is provided with a pair of securing tab portions 68, 69. As seen in FIG. 5 there are three longitudinally spaced laterally paired bearing or supporting members indicated at 71, 72; 73, 74; and 75, 76 which are formed integral with the housing 61. The bearing members 71-74 are in the form of raised cylindrical bosses while the members 75, 76 are elongated in shape to provide stop or calibration lugs for a purpose to be explained.

Clamped to the top faces of each of the bosses 71, 72 there are a pair of identical elongated single pole single throw switches having cantilevered spring arms 78, 79 of electrically conductive material such as sheet metal which extend longitudinally of the housing 61 and each carries intermediate its free end and its cantilevered mounting end a control means or switch contact member 81 and 82 respectively. Each of the spring arms 78, 79 are cantilever mounted by threaded terminal bolts 83, 84 extending through the bosses 71, 72 each bolt having its threaded end projecting from the underside of the bottom wall 63 for receiving terminal nuts 80 and being threaded into the plates 85 on the underside of the housing with contact washers 86 spaced between the bosses 71, 72 and the spring arms 78, 79.

Cooperable with the contact members 81, 82 there are fixed switch contact members 87, 88 which are spaced a defined height below the cantilevered mounting of the spring arms 30, 31 on the bearing bosses 73, 74. The contact members 87, 88 are secured to the terminal posts 91, 92 threadably engaged in holding plates 93 having their threaded ends projecting from the bottom wall 63 for receiving terminal nuts 89 therein. The free end of the switch operating arms 78, 79 are formed with semicylindrical projections 94, 95 curved upwardly in an arcuate pattern to define channels extending transversely of the arms 78, 79. A crossbeam or bar 96, in the form ofa rigid nonconducting material such as an electrical porcelain of general cylindrical configuration is snugly positioned in the arcuate channels of bent portions 94, 95 and extends across substantially the entire width of the housing 61 to spring bias the movable contacts 81, 82 into contact with fixed contacts 87, 88.

A metallic conductor collar 98, having a cylindrical construction and a central bore extending therethrough to furnish a slip fit with the crossbeam 96, is suitably fixed such as by epoxy cement to the center of the crossbeam 96 and includes a circumferential groove 99 on its outer periphery. Radial ends 97 (FIG. 5) of collar 98 are suitably welded to provide an electrically continuous path therearound. A fusible link filament or fuse wire 101 is looped around the crossbeam 96 for location within the groove 99 and the fuse wire 101 has its free ends extending through a pair of D shaped apertures 102, 103

defining a brace member 104 with the free ends electrically connected to a terminal post 105 secured to the brace 104. An oblong embossment 106 formed in the housing bottom wall 63 surrounds the apertures 102, 103 to guard the terminal post 105. The fuse wire 101 spring biases the resilient contact arms downwardly by means ofcrossbeam 96 to their full-line bowed position of FIG. 5 such that the semicylindrical projections 94, 95 engage or bottom on their respective calibration members or stop lugs 75, 76 while the fixed contacts 87, 88 are at a height to how the spring arms 78, 79 at a uniform deformation about the fulcrums' provided by contacts 87, 88. The stop lugs 75, 76 establish predetermined positioning of the spring arms 78, 79 to provide a quick calibration for the protective device and insure proper pressure between the mating contacts 81, 87 and 82, 88. This arrangement allows limited thermal expansion of the fuse wire link 11! resulting from ambient temperature conditions because the positioning of fulcrumed support contacts 87, 88 assures sufficient flexure of the spring arms 78, 79 under the bias of the crossbeam 96 to maintain the required pressure between the mating contacts.

The beam 96 has a pair of ring conductors 111, 112 formed of strips of a thin, narrow electrically conductive material, such as stainless steel, wrapped around each'end of the crossbeam with radial ends 113, 114 of the rings suitably secured as by welding as shown in FIGS. 4 and 5. A current limiting resistance member 115 which preferably comprises suitable resistance wire wound in a coiled manner about the beam 96 with one free end welded directly to the ring 112 and its other free end welded to the central collar 98. By virtue of this arrangement the current limiting resistance wire 115 is incorporated with the protective device and thus eliminates the need for providing a separate resistor in the circuit arrangement utilizing applicants device discussed below.

FIG. 6 is a schematic diagram of a range surface unit rupture protection circuit showing one application of the protective device of the present invention. Range surface units, indicated at 120, 121 and 122 may be supplied with electrical service of three-wire Edison source of power; normally of 236 volts, single phase, 60 cycle, AC which is available in a kitchen having adequate wiring. This source of power has a pair of line wires L, and L, with a voltage of 236 volts therebetween, and a grounded neutral conductor N with half voltage of 1 18 volts normally measured across any line wire L, or L and the neutral conductor N. Since the present invention relates to the control of the surface heating units, the oven and the associated wiring are not included in the circuit diagram of FIG. 6 for the sake of simplicity.

The range surface unit may be subject to rupture caused by current flowing between one of the unit heater elements 123 and its associated grounded metal sheath 124 in a concentrated area. Transformer turns 126, 128 and 130 are similar windings of a transformer and generate a net magnetic flux in a transformer core (not shown) which is proportional to the net current flowing through the windings 126, 128 and 130. In normal operation the net current is zero resulting in no magnetic flux being generated and no voltage being induced in an additional actuating winding 131. The supply lines L, and L, are shown connected through the windings 126, 128 respectively to the electrically conductive contact arms 78, 79 by means of their terminal posts 91, 92 through the normally closed paired contacts 81, 87 and 82, 88 allow current to flow to terminal bolts 83, 84 via contact arms 78, 79. The terminal bolts 83, 84 are connected to the surface units 120, 121 and 122 as shown while the neutral line N is connected through the third winding 130 and conductor 132 to the terminal element 133 and thence to the heating units. In addition, the conductor 132 is connected by conductor 134 to the actuating winding 131 and by conductor 136 to variable resistor 138 and thence to the controlling electrode 140 of an electronic switch consisting of a bidirectional thyristor or symmetrical controlled rectifier 142 such as a semiconductor device sold by Electronic Control Corporation under the trademark Quadrac. The symmetrical controlled rectifier 142 is connected in series by its main electrodes 144 and 146 to the terminal 105 of the fusible wire link 101 and thence by conductor collar 98 through the current limiting resistor 115 and conductor ring 112 to the line L When a leakage current flows from one of the sheaths 124 of the range surface unit circuits through the ground 145 of the range back to the neutral line N, the net current flowing through the windings 126, 128 and 130 no longer sums to zero, a magnetic flux is generated in the transformer core proportional to the leakage current and a voltage is induced in the actuating winding 131. The voltage in the actuating winding 131 is used to trigger the symmetrical controlled rectifier 142 via its electrode 140 allowing current flow through the fusible wire link 101 of the protective device and the current limiting resistor 115. This current flow breaks or fuses the link 101 at a predetermined value and releases the crossbeam contact spring arms 78, 79 allowing them to simultaneously spring upwardly from their downwardly bowed position of FIG. 5 to assume their unbiased normal horizontal straight shape position, indicated by the dashed line position. Thus a snap-action device is provided and in so doing withdraw the movable contacts 81, 82 spaced from the fixed contacts 87, 88 to thereby suddenly break the circuit by opening the lines L and L in unison leaving only the main line input terminal bolts 91 and 92 of the protective device energized.

It will be noted that the spring arms 78, 79 project beyond their cantilevered supports 71, 72 by means of spring arm rear extensions 148, 149 such that they overlie transverse partition 150 formed integral with central boss 151 and housing sidewalls 64, 65. The partition 150 has a central upstanding divider portion 152 which with the sidewall mullions 162, 163 provide a pair of slots for receiving the rear extensions 148, 149 whereby the spring arms 78 79 are maintained in positive or fixed spaced parallel relation. An intermediate longitudinal partition 153 insures that the crossbeam 96 is retained in its spring arm arcuate channels after the wire fuse link 101 has been fused and the crossbeam 96 is sprung to its upper dashed-line position shown in FIG. 5. The transverse partition supports shown at 154, 155 are sloped at an angle of 45 toward the sidewalls so as not to interfere with the movement of the spring arms 78, 79. Spaced partitions 157, 158, 159, 160 and 161 are provided on the underside of the housing 61 to separate the electrical wires connected to the various terminals of the protective device.

The preferred embodiment of the invention of FIGS. 4 and 5 provides quick, easy and rigid mounting of the crossbeam 96 with the spring arms 78, 79 greatly facilitating the manufacture of the circuit protective assembly. Also, it makes possible a convenient and superior means of connecting the leads of the resistance wire 115 to the conductor collar 98 and ring connector 112. In addition the fuse wire link 101 is readily secured by having its free end leads extend through holes 102, 103 in the housing and wrapped around the terminal post 105 and are held thereto by fused metal; that is, the leads and terminal post 105 are fuse bonded by fused metal to each other. The connection of the fuse wire link to its terminal is both secure and visible after the engagement of the semicylindrical projections 94, 95 with the stop lugs 75, 76.

While the fusible link protective device of the invention is shown in combination with a range surface unit rupture protection circuit applicants device may be used in other appliance applications such as, for example, the fracture detector circuit disclosed in copending application (A-! 3,5 25) and assigned to the same assignee as the instant application.

It will be apparent from the foregoing that the circuit protective device is very easily manufactured, strong and economical. It should also be apparent that the crossbeam arrangement in general and the means by which it is mounted minimize problems of insulating the terminals and the possibility of grounds or shorts.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is:

l. A fusible wire link circuit protective device for an electrical appliance comprising a housing, a pair of elongated, electrically conductive, coextending cantilevered spring arms in side-by-side relation, said spring arms mounted within said housing by terminal bolts rigidly supporting one end of each of said cantilevered spring arms adjacent to said housing on first bearing means at a first elevation, said terminal bolts adapted to be connected to the electrical appliance, a rigid crossbeam formed of electrical insulating material commonly joining the free end of each of said cantilevered spring arms together, each of said cantilevered spring arms having a movable contact carried on the underside thereof intermediate the ends of said spring arm, whereby each said spring arm is in conductive contact with its respective terminal bolt and movable contact, a pair of laterally spaced fixed contacts positioned in said housing on a second bearing means at a second elevation a defined distance below said first elevation, each of said fixed contacts adapted to be contacted by one of said spring arm movable contacts, each of said fixed contacts including a terminal post for electrical connection with a line from a power supply source, means at the midpoint of said crossbeam for receiving a fusible wire link, said fusible wire link looped over the midpoint of said crossbeam and positioned in said receiving means, said fusible wire link having its free ends fixedly secured to terminal means in said housing to spring bias each of said spring arm movable contacts into fulcrumed abutment and electrical engagement on its corresponding fixed contact, said terminal means adapted to be connected to the power supply source, a pair of laterally spaced stop lugs positioned in said housing at a third elevation a defined distance below the elevation of said fixed contacts, each said stop lug engageable with the corresponding free end of one of said spring arms to uniformly bias each of said spring arms in the same concavely downward cylindrical space curve upon securing the free ends of said fusible wire link to said terminal means, said fusible wire link becoming fusible when a predetermined electric current is passed therethrough thereby withdrawing said spring arm movable contacts from said fixed contacts in unison to' simultaneously disconnect the lines of the power supply source from the electrical appliance such that only said fixed contacts remain energized by said power supply source.

2. The fusible wire link circuit protective device as defined in claim 1 wherein said terminal means comprises a pair of terminals extending into said housing, each said spring arm free end having an aperture therein, said crossbeam having a pair of spaced detent projections thereon, each of said detent projections extending through one of said spring arm apertures whereby said spring arms are maintained in positive spaced parallel relation, said crossbeam receiving means comprising a saddlelike portion integrally formed thereon at its midpoint, said fusible wire link received in said saddlelike portion with its free ends being secured to said pair of terminals whereby said crossbeam is fixedly retained with said spring arms to bias said detent projections into contact with said stop lugs.

3. The fusible wire link circuit protective device as defined in claim 1 wherein said terminal means comprises a single terminal extending into said housing, each said spring arm free end formed with semicylindrical projections curved upwardly to define a channel extending transversely thereacross, said crossbeam having each end portion thereof received in one of said spring arm channels in complementary fashion, each said spring arms having a rear extension received in slots formed in said housing whereby said spring arms are maintained in positive spaced parallel relation, said crossbeam receiving means including a conductor collar encircling the midpoint of said crossbeam having groove means formed thereon, a resistance wire coiled about said crossbeam between said conductor means and one end of said crossbeam electrically connecting said conductor means with the free end of one of said spring arms, said fusible wire link received in said conductor groove means with its free ends secured to said single terminal whereby said crossbeam is fixedly retained in said spring arm channels to bias said spring arm projections into contact with said stop lugs.

4. A fusible link circuit protective device for an electrical appliance the combination of a box-shaped housing formed of heat and electrical insulating material and having a bottom wall, sidewalls and end walls defining a top opening, laterally paired first, second and third sets of raised bearing elements formed integrally with said housing bottom wall and arranged I in longitudinally spaced relation adjacent one end wall, the

midportion of said sidewalls, and the remaining end wall, respectively; said first, second and third sets of bearing elements having upper bearing surfaces arranged in descending order of elevation commencing from said first to said third paired bearing elements, a vertical terminal bolt extending through each of said first paired bearing elements and projecting beneath the bottom wall of said housing for electrical connection with the electrical appliance, a pair of thin resilient electrically conductive spring arms fixedly supported at one end thereof in cantilevered side-by-side relation by said terminal bolts from the upper surfaces of said first bearing elements with their other ends free to move, each said spring arm having a movable electrical contact carried thereon intermediate its free end and its cantilevered end on the underside thereof, each said spring arm providing an electrical path between its associated terminal bolt and movable contact, a pair of vertical terminal posts each having a fixed electrical contact integrally formed on the upper end thereof, each of such terminal posts extending through one of said second set of bearing elements and projecting beneath said housing bottom wall for connection with the lines of a power supply source whereby said terminal post fixed contacts are disposed at the elevation of said second set of bearing element surfaces to engage said spring arm movable contacts, each said spring arm free end having an aperture therein, a crossbeam formed of electrical insulating material positioned transverse to said spring arms and overlying the free ends thereof, said crossbeam having a planar bottom surface provided with a pair of spaced detent projections, each of said detent projections extending through one of said spring arm aligned apertures whereby said spring arms are maintained in positive spaced parallel relation, said crossbeam having a pair of transverse raised ridges spaced equidistant from the midpoint of said crossbeam defining a saddlelike portion thereon, a looped fusible wire link extending over said crossbeam and received in said saddlelike portion, said fusible wire link having its free ends fixedly secured to a pair of terminal members extending through said housing bottom wall, said fusible wire link operative to spring bias said spring arms downwardly whereby said detent projections engage, respectively, said third set of hearing elements such that said spring arm movable contacts are positioned in fulcrum electrical engagement with their associated fixed contacts whereby each of said spring arms are bowed concavely downward in the same cylindrical space curve in a preset manner, said spring arms allowing limited thermal elongation of said fusible wire link while maintaining the required contact pressure between said fixed and movable contacts, said fusible wire link becoming fusible when a predetermined electric current is passed therethrough releasing said spring arms in unison to simultaneously disconnect both lines of the power supply source from the electrical appliance such that only said fixed contacts remain energized by said power supply source.

5. A fusible link circuit protective device for an electrical appliance the combination of a box-shaped housing formed of heat and electrical insulating material and having a bottom wall, sidewalls and end walls defining a top opening, laterally paired first, second and third sets of raised bearing elements formed integrally with said housing bottom wall and arranged in longitudinally spaced relation adjacent one end wall, the midportion of said sidewalls, and the remaining end wall, respectively; said first, second and third sets of bearing elements having upper bearing surfaces arranged in descending order of elevation commencing from said first to said third set of bearing elements, a vertical terminal bolt extending through each of said first bearingelements and projecting beneath the bottom wall of said housing for electrical connection with the electrical appliance, a pair of thin resilient electrically conductive spring arms fixedly supported at one end thereof in cantilevered side-by-side relation by said terminal bolts from said first set of bearing element upper surfaces with their other ends free to move, each said spring arm having a movable electrical contact carried thereon intermediate its free end and its cantilevered end on the underside thereof, each said spring arm providing an electrical path between its associated terminal bolt and movable contact, a pair of vertical terminal posts each having a fixed electrical contact integrally formed on the upper end thereof extending through one of said second set of bearing elements and projecting beneath said housing bottom wall for connection with the lines of a power supply source whereby said terminal postfixed contacts are disposed at the elevation of said second set of bearing element surfaces to engage said spring arm movable contacts, each said spring arm having rearward extensions received in a slot formed in said housing whereby said spring arms are maintained in positive spaced parallel relation each said spring arm free end curved upwardly to form a semicylindrical projection defining an arcuate channel extending transversely thereacross, a rigid crossbar formed of electrical insulating material having a generally cylindrical configuration positioned with each end portion thereof retained in one said spring arm arcuate channels, a cylindrically shaped conductor collar encircling the midpoint of said crossbar and having a circumferential groove formed on its outer periphery, a looped fusible wire link extending over said crossbar and received in said groove for electrical connection with said collar, said fusible wire link having its free ends fixedly secured to a common terminal member extending through said housing bottom wall, said fusible wire link operative to spring bias said spring arms downwardly whereby said semicylindrical projections engage, respectively, said third set of bearing elements, said third set of bearing elements operative as stop lugs such that said spring arm movable contacts are positioned in fulcrum electrical engagement with their associated fixed contacts whereby each of said spring arms are bowed concavely downward in the same cylindrical space curve in a preset manner, said spring arms allowing limited thermal elongation of said fusible wire link while maintaining the required contact pressure between said fixed and movable contacts, a ring conductor located on each end of said crossbar in electrical contact with the arcuate channel of its associated spring arm, a resistance wire wound on said crossbar between said conductor collar and one of said ring conductors and having its free ends electrically connected to said collar and said ring respectively, thereby providing a current limiting resistor for said fusible wire link, said fusible wire link becoming fusible when a predetermined electric current is passed therethrough releasing said spring arms in unison to simultaneously disconnect both lines of the power supply circuit.

' :r s x 

1. A fusible wire link circuit protective device for an electrical appliance comprising a housing, a pair of elongated, electrically conductive, coextending cantilevered spring arms in side-by-side relation, said spring arms mounted within said housing by terminal bolts rigidly supporting one end of each of said cantilevered spring arms adjacent to said housing on first bearing means at a first elevation, said terminal bolts adapted to be connected to the electrical appliance, a rigid crossbeam formed of electrical insulating material commonly joining the free end of each of said cantilevered spring arms together, each of said cantilevered spring arms having a movable contact carried on the underside thereof intermediate the ends of said spring arm, whereby each said spring arm is in conductive contact with its respective terminal bolt and Movable contact, a pair of laterally spaced fixed contacts positioned in said housing on a second bearing means at a second elevation a defined distance below said first elevation, each of said fixed contacts adapted to be contacted by one of said spring arm movable contacts, each of said fixed contacts including a terminal post for electrical connection with a line from a power supply source, means at the midpoint of said crossbeam for receiving a fusible wire link, said fusible wire link looped over the midpoint of said crossbeam and positioned in said receiving means, said fusible wire link having its free ends fixedly secured to terminal means in said housing to spring bias each of said spring arm movable contacts into fulcrumed abutment and electrical engagement on its corresponding fixed contact, said terminal means adapted to be connected to the power supply source, a pair of laterally spaced stop lugs positioned in said housing at a third elevation a defined distance below the elevation of said fixed contacts, each said stop lug engageable with the corresponding free end of one of said spring arms to uniformly bias each of said spring arms in the same concavely downward cylindrical space curve upon securing the free ends of said fusible wire link to said terminal means, said fusible wire link becoming fusible when a predetermined electric current is passed therethrough thereby withdrawing said spring arm movable contacts from said fixed contacts in unison to simultaneously disconnect the lines of the power supply source from the electrical appliance such that only said fixed contacts remain energized by said power supply source.
 2. The fusible wire link circuit protective device as defined in claim 1 wherein said terminal means comprises a pair of terminals extending into said housing, each said spring arm free end having an aperture therein, said crossbeam having a pair of spaced detent projections thereon, each of said detent projections extending through one of said spring arm apertures whereby said spring arms are maintained in positive spaced parallel relation, said crossbeam receiving means comprising a saddlelike portion integrally formed thereon at its midpoint, said fusible wire link received in said saddlelike portion with its free ends being secured to said pair of terminals whereby said crossbeam is fixedly retained with said spring arms to bias said detent projections into contact with said stop lugs.
 3. The fusible wire link circuit protective device as defined in claim 1 wherein said terminal means comprises a single terminal extending into said housing, each said spring arm free end formed with semicylindrical projections curved upwardly to define a channel extending transversely thereacross, said crossbeam having each end portion thereof received in one of said spring arm channels in complementary fashion, each said spring arms having a rear extension received in slots formed in said housing whereby said spring arms are maintained in positive spaced parallel relation, said crossbeam receiving means including a conductor collar encircling the midpoint of said crossbeam having groove means formed thereon, a resistance wire coiled about said crossbeam between said conductor means and one end of said crossbeam electrically connecting said conductor means with the free end of one of said spring arms, said fusible wire link received in said conductor groove means with its free ends secured to said single terminal whereby said crossbeam is fixedly retained in said spring arm channels to bias said spring arm projections into contact with said stop lugs.
 4. A fusible link circuit protective device for an electrical appliance the combination of a box-shaped housing formed of heat and electrical insulating material and having a bottom wall, sidewalls and end walls defining a top opening, laterally paired first, second and third sets of raised bearing elements formed integrally with said housing bottom wall and arranged in longitudinally spaced relation adjacent one end wall, the midportion of said sidewalls, and the remaining end wall, respectively; said first, second and third sets of bearing elements having upper bearing surfaces arranged in descending order of elevation commencing from said first to said third paired bearing elements, a vertical terminal bolt extending through each of said first paired bearing elements and projecting beneath the bottom wall of said housing for electrical connection with the electrical appliance, a pair of thin resilient electrically conductive spring arms fixedly supported at one end thereof in cantilevered side-by-side relation by said terminal bolts from the upper surfaces of said first bearing elements with their other ends free to move, each said spring arm having a movable electrical contact carried thereon intermediate its free end and its cantilevered end on the underside thereof, each said spring arm providing an electrical path between its associated terminal bolt and movable contact, a pair of vertical terminal posts each having a fixed electrical contact integrally formed on the upper end thereof, each of such terminal posts extending through one of said second set of bearing elements and projecting beneath said housing bottom wall for connection with the lines of a power supply source whereby said terminal post fixed contacts are disposed at the elevation of said second set of bearing element surfaces to engage said spring arm movable contacts, each said spring arm free end having an aperture therein, a crossbeam formed of electrical insulating material positioned transverse to said spring arms and overlying the free ends thereof, said crossbeam having a planar bottom surface provided with a pair of spaced detent projections, each of said detent projections extending through one of said spring arm aligned apertures whereby said spring arms are maintained in positive spaced parallel relation, said crossbeam having a pair of transverse raised ridges spaced equidistant from the midpoint of said crossbeam defining a saddlelike portion thereon, a looped fusible wire link extending over said crossbeam and received in said saddlelike portion, said fusible wire link having its free ends fixedly secured to a pair of terminal members extending through said housing bottom wall, said fusible wire link operative to spring bias said spring arms downwardly whereby said detent projections engage, respectively, said third set of bearing elements such that said spring arm movable contacts are positioned in fulcrum electrical engagement with their associated fixed contacts whereby each of said spring arms are bowed concavely downward in the same cylindrical space curve in a preset manner, said spring arms allowing limited thermal elongation of said fusible wire link while maintaining the required contact pressure between said fixed and movable contacts, said fusible wire link becoming fusible when a predetermined electric current is passed therethrough releasing said spring arms in unison to simultaneously disconnect both lines of the power supply source from the electrical appliance such that only said fixed contacts remain energized by said power supply source.
 5. A fusible link circuit protective device for an electrical appliance the combination of a box-shaped housing formed of heat and electrical insulating material and having a bottom wall, sidewalls and end walls defining a top opening, laterally paired first, second and third sets of raised bearing elements formed integrally with said housing bottom wall and arranged in longitudinally spaced relation adjacent one end wall, the midportion of said sidewalls, and the remaining end wall, respectively; said first, second and third sets of bearing elements having upper bearing surfaces arranged in descending order of elevation commencing from said first to said third set of bearing elements, a vertical terminal bolt extending through each of said first bearing elements and projecting beneath the bottom wall of said housing for elEctrical connection with the electrical appliance, a pair of thin resilient electrically conductive spring arms fixedly supported at one end thereof in cantilevered side-by-side relation by said terminal bolts from said first set of bearing element upper surfaces with their other ends free to move, each said spring arm having a movable electrical contact carried thereon intermediate its free end and its cantilevered end on the underside thereof, each said spring arm providing an electrical path between its associated terminal bolt and movable contact, a pair of vertical terminal posts each having a fixed electrical contact integrally formed on the upper end thereof extending through one of said second set of bearing elements and projecting beneath said housing bottom wall for connection with the lines of a power supply source whereby said terminal post fixed contacts are disposed at the elevation of said second set of bearing element surfaces to engage said spring arm movable contacts, each said spring arm having rearward extensions received in a slot formed in said housing whereby said spring arms are maintained in positive spaced parallel relation each said spring arm free end curved upwardly to form a semicylindrical projection defining an arcuate channel extending transversely thereacross, a rigid crossbar formed of electrical insulating material having a generally cylindrical configuration positioned with each end portion thereof retained in one said spring arm arcuate channels, a cylindrically shaped conductor collar encircling the midpoint of said crossbar and having a circumferential groove formed on its outer periphery, a looped fusible wire link extending over said crossbar and received in said groove for electrical connection with said collar, said fusible wire link having its free ends fixedly secured to a common terminal member extending through said housing bottom wall, said fusible wire link operative to spring bias said spring arms downwardly whereby said semicylindrical projections engage, respectively, said third set of bearing elements, said third set of bearing elements operative as stop lugs such that said spring arm movable contacts are positioned in fulcrum electrical engagement with their associated fixed contacts whereby each of said spring arms are bowed concavely downward in the same cylindrical space curve in a preset manner, said spring arms allowing limited thermal elongation of said fusible wire link while maintaining the required contact pressure between said fixed and movable contacts, a ring conductor located on each end of said crossbar in electrical contact with the arcuate channel of its associated spring arm, a resistance wire wound on said crossbar between said conductor collar and one of said ring conductors and having its free ends electrically connected to said collar and said ring respectively, thereby providing a current limiting resistor for said fusible wire link, said fusible wire link becoming fusible when a predetermined electric current is passed therethrough releasing said spring arms in unison to simultaneously disconnect both lines of the power supply circuit. 